How could someone who stole, via fraud or other methods, multi-billions of dollars cumulatively from thousands of people, that is virtually impossible to repay even in several lifetimes (and he is imprisoned), do a complete teshuva and go to Gan Eden as soon as he comes to the Olom Haemes?

I don’t know why you had to bring up a specific example and mention names but anyhow, אין דבר עומד בפני התשובה. Nebuzaradan who was in charge of destroying the Beis Hamikdash saw the boiling blood of Zechariah and in order to try calm it down, slaughtered thousands and thousands of Yidden on it. He saw that it didn’t stop until he called out if he should slaughter more Yidden, then the blood stopped boiling. As soon as he saw this he trembled how it took so many lives for atonement of one man. What will happen to him for slaughtering so many! He immediately went to convert to Judaism.
Also the story of Rabbi Elazar ben Dordya who didn’t leave one harlot untouched. When he heard that his teshuva will not be accepted,he cried out to the mountains, the sky, the sun moon etc.. that they should ask for Rachamim on his behalf. Not being able to get a positive reply, he saw that it was up to him. He sat and cried out until his Neshama departed his body, and a voice came out that he was welcomed to Olam Haba.

And by the way, there are bigger aveiros than stealing money. Causing someone to do an aveira is worse I think, since you’re affecting the person spiritually and you don’t even gain from it (usually). And I would think that hurting people emotionally could also be considered worse than stealing money.

But one can do teshuva for those things as well. If you kill someone, c”v, you can still do teshuva even though the person can’t be brought back to life. Doing teshuva doesn’t necessarily mean undoing the deed. When it’s possible to do so, you must do so, but when it’s not possible, then that is not a requirement of your teshuva. Your requirement is to do the most that you possibly can to undo the damage – no more and no less.

If you stole money from people and it’s not possible to return it, then you should at least try to ask mechila if possible. If it’s not possible, then you should ask a sheilah as to how to do teshuva.

I have heard some interesting stories regarding people who did really big aveiros bein adam l’chaveiro that couldn’t be undone and they asked sheilahs about how to do teshuva and were given interesting answers. It usually had to do with giving back to the tzibor in some way.

One story had to do with a baalas teshuva who had been oiver on gilui arayos and was told to build a mikva.

At the neshomoh level, a Yid who is not frum is no different from one who is. At that level, every single neshomoh is a child of HKB”H, as the Gemora states clearly (בבא בתרא דף י’ ע”א) that whether we are fulfilling Ratzon Hashem or not, בין כך ובין כך איקרי בנים. While I do not need to consider the Yid who is not keeping mitzvos a suitable shidduch for my child, I have no authority to address the connection he has to HKB”H. That matter is purely בין אדם למקום, and that is territory where I cannot trespass.

For that matter, the seforim tell us that teshuvah for anything is possible. However, someone else’s teshuvah is not accessible to me. I cannot base anything I do on it, and I cannot ever really know what is going on in that realm. If the OP’s question is otherwise expressed as: If I commit a major theft of enormous sums of money, which I will never be able to compensate, what teshuvah can I do? Valid question, since we are told that a prerequisite for teshuvah for גנבה or גזלה is the repayment. If the question is worrying about Madoff, or any other such individual who embezzled major monies, I suggest we redirect. If my personal חשבון הנפש is meaningful at all, I have enough work to do on myself, and have no business minding someone else’s חשבון הנפש.

I once asked a christian who was protelizing, about someone who was a murderer , Had kidnapped someone and committed a gruesome crime (This was a national news story) if they would accept “Him” , the frankly admitted that was the christian way, but they themselves admitted it would be hard for them to accept it.

I really dont think Madoff could ever do enough tshuva for his crimes, besides stealing the money, it was a massive chilul hashem and he wasnt even religious

Today is Rosh Chodesh Ellul. That should send a shudder through each of us : How are we going to do tshuva for our own avairos. It is hardly the time to speculate the nature of tshuva others need to do.

If a person doesn’t have a way to return the stolen money either because he doesn’t know who it belongs to or another reason then the seforim say he should do community service work so that whoever he stole it from will gain from his work and it will be like his pay

Or he can give it to tzedaka and Hashem Has A Way For It Get Back To The Person He Stole It from